Wokflow triggering after completion

I have developed workflow for sale order creation. Workflow is working fine there is just one problem I am facing. Once all approvers have apporved worklfow gets completed. Before that I have created an activity step which deletes billing block and I have used task in this step to delete billing block. Its a background task. Now when activity step is executed change event is triggered and same mail is sent to all approvers all over again. Have tried to change condition in SWB_COND but nothing is working. Is there anyway I can avoid this situation? Help is appreciated.

I have used the same. But i was wondering if there is any other way by which we can stop workflow from triggering at all. Will definitely use SWEINST and check if the event can be stopped from triggering. Thanks for your suggestion and time.